Impact

Affected versions

• 0.3.60 and earlier.
• 1.0.0 to 1.2.9 when used with the Ruby data source (tzinfo-data).

Vulnerability

With the Ruby data source (the tzinfo-data gem for tzinfo version 1.0.0 and
later and built-in to earlier versions), time zones are defined in Ruby files.
There is one file per time zone. Time zone files are loaded with require on
demand. In the affected versions, TZInfo::Timezone.get fails to validate
time zone identifiers correctly, allowing a new line character within the
identifier. With Ruby version 1.9.3 and later, TZInfo::Timezone.get can be
made to load unintended files with require, executing them within the Ruby
process.

For example, with version 1.2.9, you can run the following to load a file with
path /tmp/payload.rb:

TZInfo::Timezone.get(\"foo\
/../../../../../../../../../../../../../../../../tmp/payload\")

The exact number of parent directory traversals needed will vary depending on
the location of the tzinfo-data gem.

TZInfo versions 1.2.6 to 1.2.9 can be made to load files from outside of the
Ruby load path. Versions up to and including 1.2.5 can only be made to load
files from directories within the load path.

This could be exploited in, for example, a Ruby on Rails application using
tzinfo version 1.2.9, that allows file uploads and has a time zone selector
that accepts arbitrary time zone identifiers.
The CVSS score and severity have been set on this basis.

Versions 2.0.0 and later are not vulnerable.

Patches

Versions 0.3.61 and 1.2.10 include fixes to correctly validate time zone
identifiers.

Note that version 0.3.61 can still load arbitrary files from the Ruby load
path if their name follows the rules for a valid time zone identifier and the
file has a prefix of tzinfo/definition within a directory in the load path.
For example if /tmp/upload was in the load path, then
TZInfo::Timezone.get('foo') could load a file with path
/tmp/upload/tzinfo/definition/foo.rb. Applications should ensure that
untrusted files are not placed in a directory on the load path.

Workarounds

As a workaround, the time zone identifier can be validated before passing to
TZInfo::Timezone.get by ensuring it matches the regular expression
\\A[A-Za-z0-9+\\-_]+(?:\\/[A-Za-z0-9+\\-_]+)*\\z.